This invention relates to the preparation of a ceramic honeycomb structure having channels that are selectively sealed at alternate faces of the honeycomb. The honeycombs are useful in a variety of filtering, separating, or concentrating operations in which a work fluid or component thereof is intended to pass through the walls of the channels.
The use of ceramic honeycomb structures as fluid filters, particulate traps, or catalytic converters is longstanding. In such traditional uses of a ceramic honeycomb, the existence of a liquid head or pressure gradient is employed to drive a fluid through the end-to-end channels of the honeycomb or, in the case of some gases, through the channel walls themselves, where contact is effected with the high surface area of the ceramic substrate or with catalytic materials deposited thereon. See, for example, U.S. Pat. No. 4,631,267 (issued Dec. 23, 1986, to Lachman et al) disclosing preparation of ceramic honeycomb catalyst support structures designed for catalytic conversion of gases at sites along the walls of the open channels, and U.S. Pat. No. 4,283,210 (issued Aug. 11, 1981, to Mochida et al) disclosing a ceramic honeycomb filter designed for passage of the work gas through the channel walls.
In those ceramic honeycomb structures designed for passage of the work gas or some component thereof through the channel walls, the otherwise open channel must be selectively and alternately sealed at one end or the other to prevent the gas from merely passing through the channel itself. Generally, the preparation of a honeycomb with such alternately sealed channels cannot be accomplished in a single extrusion step and requires at least one further operation performed on a green or fired open-channelled honeycomb. For example, such a process is shown in U.S. Pat. No. 4,283,210, in which the selective sealing of channels is effected by bending and bonding the partition walls of given channels at one of the end faces of a green ceramic honeycomb body, and performing the same operation to the remaining channels at the other end face of the body.
Published European Patent Specification No. 42,301 also discloses a ceramic honeycomb body having selectively sealed channels prepared by fitting a sealing member onto each end face of a green open-channeled honeycomb body, each sealing member having a plurality of openings corresponding to alternate channel openings of the honeycomb such that each channel will be blocked at one or the other of its ends. It is taught that the sealing members and the green honeycomb are separately dried before the sealing members are fitted to the honeycomb body itself, preferably by means or an organic adhesive, a glass material, or a ceramic material, followed by standard firing of the composite so formed. U.S. Pat. No. 4,329,162 also discloses ceramic honeycomb filters in which selective seals are provided to the inlet and outlet channels by injecting a sinterable material or other sealing cement into the appropriate ends of the channels to form a "checkerboard" array of open/closed channels at each end face.
Although the art is familiar with methods for preparing ceramic honeycomb structures with selectively sealed channels, there remains a need for other practical methods for forming integral, hermetically sealed caps at the channel ends.